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Don't wash those fossils!
Standard museum practice can wash away DNA.
1.Washing, brushing and varnishing fossils — all standard conservation
treatments used by many fossil hunters and museum curators alike — vastly
reduces the chances of recovering ancient DNA.
2.Instead, excavators should be handling at least some of their bounty with
gloves, and freezing samples as they are found, dirt and all, concludes a paper
in the Proceedings of the National Academy of Sciences today.
3.Although many palaeontologists know anecdotally that this is the best way
to up the odds of extracting good DNA, Eva-Maria Geigl of the Jacques Monod
Institute in Paris, France, and her colleagues have now shown just how important
conservation practices can be.This information, they say, needs to be hammered
home among the people who are actually out in the field digging up bones.
4.Geigl and her colleagues looked at 3,200-year-old fossil bones belonging to
a single individual of an extinct cattle species, called an aurochs.The fossils
were dug up at a site in France at two different times — either in 1947, and
stored in a museum collection, or in 2004, and conserved in sterile conditions
at -20 oC.
5.The team's attempts to extract DNA from the 1947 bones all failed.The newly
excavated fossils, however, all yielded DNA.
6.Because the bones had been buried for the same amount of time, and in the
same conditions, the conservation method had to be to blame says Geigl."As much
DNA was degraded in these 57 years as in the 3,200 years before," she says.
Wash in, wash out
7.Because many palaeontologists base their work on the shape of fossils
alone, their methods of conservation are not designed to preserve DNA, Geigl
explains.
8.The biggest problem is how they are cleaned.Fossils are often washed
together on-site in a large bath, which can allow water — and contaminants in
the form of contemporary DNA — to permeate into the porous bones."Not only is
the authentic DNA getting washed out, but contamination is getting washed in,"
says Geigl.
9.Most ancient DNA specialists know this already, says Hendrik Poinar, an
evolutionary geneticist at McMaster University in Ontario, Canada.But that
doesn't mean that best practice has become widespread among those who actually
find the fossils.
10.Getting hold of fossils that have been preserved with their DNA in mind
relies on close relationships between lab-based geneticists and the excavators,
says palaeogeneticist Svante P bo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany.And that only occurs in exceptional cases, he
says.
11.P bo's team, which has been sequencing Neanderthal DNA, continually faces
these problems."When you want to study ancient human and Neanderthal remains,
there's a big issue of contamination with contemporary human DNA," he says.
12.This doesn't mean that all museum specimens are fatally flawed, notes P
bo.The Neanderthal fossils that were recently sequenced in his own lab, for
example, had been part of a museum collection treated in the traditional way.But
P bo is keen to see samples of fossils from every major find preserved in line
with Geigl's recommendations — just in case.
Warm and wet
13.Geigl herself believes that, with cooperation between bench and field
researchers, preserving fossils properly could open up avenues of discovery that
have long been assumed closed.
14.Much human cultural development took place in temperate regions.DNA does
not survive well in warm environments in the first place, and can vanish when
fossils are washed and treated.For this reason, Geigl says, most ancient DNA
studies have been done on permafrost samples, such as the woolly mammoth, or on
remains sheltered from the elements in cold caves — including cave bear and
Neanderthal fossils.
15.Better conservation methods, and a focus on fresh fossils, could boost DNA
extraction from more delicate specimens, says Geigl.And that could shed more
light on the story of human evolution.
(640 words nature )
Glossary
Palaeontologists 古生物学家
Aurochs 欧洲野牛
Neanderthal (人类学)尼安德特人，旧石器时代的古人类。
Permafrost (地理)永冻层
Questions 1-6
Answer the following questions by using NO MORE THAN THREE WORDS for each
answer.
1.How did people traditionally treat fossils?
2.What suggestions do Geigl and her colleagues give on what should be done
when fossils are found?
3.What problems may be posed if fossil bones are washed on-site? Name
ONE.
4.What characteristic do fossil bones have to make them susceptible to be
contaminated with contemporary DNA when they are washed?
5.What could be better understood when conservation treatments are
improved?
6.The passage mentioned several animal species studied by researchers.How
many of them are mentioned?
Questions 7-11
Do the following statements agree with the information given in the passage?
Please write TRUE if the statement agrees with the writer FALSE if the statement
does not agree with the writer NOT GIVEN if there is no information about this
in the passage.
7.In their paper published in the Proceedings of the National Academy of
Sciences，Geigl and her colleagues have shown what conservation practices should
be followed to preserve ancient DNA.
8.The fossil bones that Geigl and her colleagues studied are all from the
same aurochs.
9.Geneticists don't have to work on site.
10.Only newly excavated fossil bones using new conservation methods suggested
by Geigl and her colleagues contain ancient DNA.
11.Paabo is still worried about the potential problems caused by treatments
of fossils in traditional way.
Questions 12-13
Complete the following the statements by choosing letter A-D for each
answer.
12.“This information” in paragraph 3 indicates:
[A] It is critical to follow proper practices in preserving ancient DNA.
[B] The best way of getting good DNA is to handle fossils with gloves.
[C] Fossil hunters should wear home-made hammers while digging up bones.
[D] Many palaeontologists know how one should do in treating fossils.
13.The study conducted by Geigl and her colleagues suggests:
[A] the fact that ancient DNA can not be recovered from fossil bones
excavated in the past.
[B] the correlation between the amount of burying time and that of the
recovered DNA.
[C] the pace at which DNA degrades.
[D] the correlation between conservation practices and degradation of
DNA.
1. A European spacecraft took off today to spearhead the search for another
"Earth" among the stars.
2. The Corot space telescope blasted off aboard a Russian Soyuz rocket from
the Baikonur cosmodrome in Kazakhstan shortly after 2.20pm.
3. Corot, short for convection rotation and planetary transits, is the first
instrument capable of finding small rocky planets beyond the solar system. Any
such planet situated in the right orbit stands a good chance of having liquid
water on its surface, and quite possibly life, although a leading scientist
involved in the project said it was unlikely to find "any little green men".
4. Developed by the French space agency, CNES, and partnered by the European
Space Agency (ESA), Austria, Belgium, Germany, Brazil and Spain, Corot will
monitor around 120,000 stars with its 27cm telescope from a polar orbit 514
miles above the Earth. Over two and a half years, it will focus on five to six
different areas of the sky, measuring the brightness of about 10,000 stars every
512 seconds.
5. "At the present moment we are hoping to find out more about the nature of
planets around stars which are potential habitats. We are looking at habitable
planets, not inhabited planets. We are not going to find any little green men,"
Professor Ian Roxburgh, an ESA scientist who has been involved with Corot since
its inception, told the BBC Radio 4 Today programme.
6. Prof Roxburgh said it was hoped Corot would find "rocky planets that could
develop an atmosphere and, if they are the right distance from their parent
star, they could have water".
7. To search for planets, the telescope will look for the dimming of
starlight caused when an object passes in front of a star, known as a "transit".
Although it will take more sophisticated space telescopes planned in the next 10
years to confirm the presence of an Earth-like planet with oxygen and liquid
water, Corot will let scientists know where to point their lenses.
8. Measurements of minute changes in brightness will enable scientists to
detect giant Jupiter-like gas planets as well as small rocky ones. It is the
rocky planets - that could be no bigger than about twice the size of the Earth -
which will cause the most excitement. Scientists expect to find between 10 and
40 of these smaller planets.
9. Corot will also probe into stellar interiors by studying the acoustic
waves that ripple across the surface of stars, a technique called
"asteroseismology".
10. The nature of the ripples allows astronomers to calculate a star’s
precise mass, age and chemical composition.
11. "A planet passing in front of a star can be detected by the fall in light
from that star. Small oscillations of the star also produce changes in the light
emitted, which reveal what the star is made of and how they are structured
internally. This data will provide a major boost to our understanding of how
stars form and evolve," Prof Roxburgh said.
12. Since the discovery in 1995 of the first "exoplanet" - a planet orbiting
a star other than the Sun - more than 200 others have been found by ground-based
observatories.
13. Until now the usual method of finding exoplanets has been to detect the
"wobble" their gravity imparts on parent stars. But only giant gaseous planets
bigger than Jupiter can be found this way, and they are unlikely to harbour
life.
14. In the 2010s, ESA plans to launch Darwin, a fleet of four or five
interlinked space telescopes that will not only spot small rocky planets, but
analyse their atmospheres for signs of biological activity.
15. At around the same time, the US space agency, Nasa, will launch
Terrestrial Planet Finder, another space telescope designed to locate Earth-like
planets.
Choose the appropriate letter from A-D for question 1.
1. Corot is an instrument which
(A) can help to search for certain planets
(B) is used to find planets in the orbit
(C) can locate planets with human beings
(D) can spot any planets with water.
Do the following statements agree with the information given in the reading
passage? For questions 2-5 write
TRUE if the statement agrees with the information
FALSE if the statement contraicts the information
NOT GIVEN if there is no information on this in the passage
2. Scientists are trying to find out about the planets that can be
inhabited.
3. BBC Radio 4 recently focuses on the broadcasting of Corot.
4. Passing objects might cause a fall in light.
5. Corot can tell whether there is another Earth-like planet.
Based on your reading of the passage, complete the sentences below with words
taken from the passage. Use NO MORE THAN THREE WORDS for each answer.
With measurements, scientists will be able to search for some gaseous and
rocky planets. They will be extremely excited if they can discover some small 6.
__________, the expected number of which could be up to 7. __________ .
Corot will enable scientists to study the 8. __________ of stars. In this
way, a star’s mass, age and chemical composition can be calculated.
According to Prof Roxburgh, changes in light can be caused by passing planets
or star 9. __________. The related statistics can gain us a better 10.
__________ of the star formation and evolvement.
Observatories have found many exoplanets, which are 11. __________ other
stars than the Sun. The common way used in finding exoplanets can only detect
huge gas planets, which do not 12. ___________ .
With the launching of Darwin, astronomers will be able to analyse whether
those rocky planets have 13. __________ for life.
